Sealing glasses may be used in sodium/sulfur or sodium/metal halide batteries to seal ceramic components together. The components can include an electrically insulating alpha-alumina collar and an ion-conductive electrolyte beta-alumina tube. The sealing glass should join ceramic components and maintain the seal by having proper wetting behavior, a similar thermal expansion property, and good strength, among other requirements. During sealing, ionic interdiffusion between the glass and the ceramic components can occur, leading to undesirable effects, such as an increase in cell resistance, and devitrification of the glass, which can cause a change in the thermal expansion property of the sealing glass, and contribute to seal failure.
A sealing glass should withstand high temperatures and corrosive environments. During operation of the battery, the sealing glass may come into contact with molten or gaseous sodium or halides of various compositions, such as tetrachloroaluminate, which can corrode the glass and break down the seal. Most of the sealing glasses may not be capable of resisting sodium and halide exposure at operating temperatures, and may therefore corrode. In general, currently available sealing glasses may not meet the complex set of requirements necessary in a sodium battery operated at 300 to 400 degrees Celsius, for an extended period of time, which can be as long as 20 years.
With these considerations in mind, it may be desirable to identify a new sealing glass composition that has properties and characteristics that beneficially differ from some of the materials that are currently available.